Electromagnetic device



Jan. 13, 1948, o. 1.. TAYLOR ELECTROMAGNETIC DEVICE Filed Feb. 28, 1947 INVENTOR Owen L. Way/0F.

BY 6 l W WITNESSES:

A ORNEY Patented Jan. 13, 1948 ELECTROMAGNETIC DEVICE Owen L. Taylor, Wilklnsburg, Pa., asslgnor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application February 28, 1942, Serial No. 731,461

6 Claims.

My invention relates to electromagnetic devices such as contactors, line starters, switches or relays, to be operated by alternating current and it has for its main object to provide simple, reliable and space saving means for securing a quiet operation of such devices.

When alternating-current magnets in switches or the like devices are used, for instance, in public buildings, X-ray laboratories or radio studios, the chattering or humming noise usually incident to the performance of such devices is often objectionable. It has, therefore, been attempted to eliminate this noise by a special design of the electromagnetic device or of the appertaining electric circuits. The known devices of silent performance, however, are relatively expensive and require additional space as compared with conventional alternating-current devices of otherwise similar design and rating. For instance, in a known alternating-current device of quiet performance, the magnetizing coils are energized through rectifiers so that the magnet proper is energized by unidirectional, constant flux. While this known device is free of chattering or humming noise, it requires more space than ordinary alternating-current magnets. This is due to the fact that the rectifiers must be relatively large because they are called upon to provide a rectifled current of suflicient magnitude to produce the magnetization required to switch the electromagnet from the open or dropped-E position into the closed or picked-up position. The known device requires also the provision of coils on the two outer legs of a generally E-shaped magnet. Consequently, the coils project away from the magnet structure proper and thus render the over-all space also larger than otherwise necessary.

According to another known device for quiet operation with alternating current, two separate coil circuits are provided, one to operate with alternating current for picking-up and the other with full-wave rectified current for holding the device closed. Aside from the fact that such a device requires relatively large coil space because of the separate coil circuits, two rectifier units in conjunction with a mid-tapped transformer or instead four bridge-connected rectifier units are needed so that the device is appreciably more expensive and larger than an otherwise similar device without the noise-eliminating features.

It is, therefore, a more specific object of my invention to provide an alternating-current magcompared with the known devices just mentioned.

In order to achieve these objects and in accordance with a. feature of the invention, 1 provide an electromagnetic device with two-series connected coils arranged on the magnet structure for cumulative magnetization, and connect two valve or rectifier means, in series with each other across the two coils so as to form a closed circuit together therewith. I further provide the device with contact means for passing an alternating-current through one of the two coils, or a portion thereof, in order to provide the relatively high air-gap magnetization required to move the armature of the device from the open to the closed position. I also equip the electromagnetic device with a holding contact which is controlled by the armature and connects the above-mentioned closed coil circuit to the alternating-current terminals of the device so that the rectifier circuit is put into operation after the picking up or a device and then operates to provide a reduced holding current for the seriesconnected coils. The coils are so rated that, when alternately energized by unidirectional current net of quiet operation in which the means used supplied through the respective two valve means, the magnetization of the device is below the value required for the picking up of the relay, but is sufficient to hold the relay in the closed position. According to another feature of the invention and in conjunction with th foregoing, I dispose the series-connected coils of the device on the center leg of a substantially E-shaped magnetic structure so that the fluxes induced in the center leg by the intermittent magnetization of the respective coils have the same direction. Although the two coils are energized by intermittent current, one coil during one-half wave period of the alternating current and the other during the other half-wave period, the relatively large time constant of the magnetic structure has the effect of maintaining a virtually uninterrupted magnetic flux although neither a midtapped transformer nor a rectifier bridge are employed.

These and other features of my invention will be apparent from the embodiments illustrated in the drawing and described hereinafter. In the drawing, Figure 1 is a schematic representation of the magnetic circuit appertaining to a device according to the invention and shows also a holding contact associated with the armature of the device. I

Fig. 2 is the diagram of a control circuit for a device according to Fig. 1, and

'Fig. 3 represents another embodiment of a control circuit for a similar device.

According to Fig. 1, the electromagnetic device has a magnetic circuit composed of a substantially E'-shaped magnet structure I and an armature 2. The structure I and the armature 2 consist of laminated magnetizable. material of relatively high permeability, low coercive force and low remanence as customary for alternating-current magnets. The magnet structure I has a center le 3 provided with windings 4. These windings comprise two series-connected coils as will be explained below with reference to Figs. 2 and 3. The armature 2 is movable relative to the stationary structure I and is guided relative to the structure I, for instance by means of the illustrated rod 5. This rod connects a movable holding contact 6 with the armature for engagement with a stationary contact assembly I. The armature movement serves to operate some mechanism or main contact assembly which is not illustrated because it may have any known design and performance and does not form an essential part of the invention proper.

A magnetic device of the general type lust described is represented in Figs. 2 and 3, mainly by a schematical representation or the center leg 3 with its coil and a likewise schematical representation of the armature 2 with the appertaining contact 5.

According to Fig. 2, the windings generally denoted in Fig. 1 by numeral 4, are composed of three series-connected coils 4|, 42 and 43. Coils 4| and 42 are the main coils and operate cumulatively, that is the magnetic fluxes induced by these coils in the leg 3 are in the same direction. The midpoint 8 of coils 4| and 42 is attached to a terminal Ti of the device for connection to the lead Ll of the alternating-current line. Two rectifier or valve means and H consisting for instance of dry or junction type rectiflers, such as copper oxide rectifiers, are connected in series relation to each other across the two coils 4| and 42 so that a closed circuit is formed which includes in series the coil 4|, rectifier i0, rectifier II and coil 42. An impedance member, f .r instance an ohmic resistor I2, has one can connected to the closed circuit at a point l3 between the valve means in and II. The other end of resistor i2 is connected in series with the normally open holding contact 6 and also in series with a normally closed stop contact i4 to another terminal T2 of the device for attachment to the other lead L2 of the alternating-current line. A normally open start contact I5 is connected, on the one hand, to a point i6 between the stop contact i4 and the holding contact 6, and on the other hand, to the free end of the auxiliary coil 43.

The illustration in Fig. 2 represents the abovedescribed device in deenergized condition. In order to cause the device to pick up or close, the start contact I5 is temporarily closed. This completes the alternating-current circuit Ti-8- 42-43-i5-I4-T2. Consequently, an alternatingcurrent passes serially through the coils-42 and 43. The alternating magnetization thus induced in the device is of sufilcient strength to cause attraction of the armature 2 toward the stationary magnet structure. When the armature 2 reaches its picked-up position, the holding contact 6 closes and completes a rectifier circuit which extends from terminal T| in parallel to both coils 4| and 42 and both appertaining rectifiers i2 and II, respectively, to point i3 and thence through the resistor l2 and the closed holding contact 6 to the stop contact 4 and the terminal T2. During on'e-half wave 01' the alternating-current cycle, the current flows from terminal Tl through coil 4| and rectifier |l while the coil 42 is not excited, while in thesubsequent halt-wave period the current flows from terminal Tl through coil 42 and rectifier while coil 4| remains unexcited. Since the fluxes induced by-the two coils 4| and 42 are of the same direction and by virtue oi the time lag in the magnetic circuit of the device, a continuous magnetization is maintained so that the armature remains held in picked up position when thereafter the start contact I! opens. 42 is rated, by a proper selection of the resistance value for resistor l2 and a proper choice of the ampere turns for coils 4| and 42, so that the magnetization of the magnetic circuit after the opening of the start contact II is sufllcient for maintaining the armature in picked up position, but is below the value of magnetization necessary ior moving the armature against its gravity or other bias from the open to the closed position. Consequently, the continuous load on the rectlfiers i0 and II is relatively small so that these rectifiers have a much smaller rating in size than would otherwise be necessary. Due to the fact that the coils are all located on the center leg 3 of the stationary structure I, no coil space is needed in addition to that determined by the winding space between the outer legs or the structure.

It will be noted that during the closing interval, the alternating-current flows substantiaily only through the coils 42 and 43, although a small rectified current may also flow through coil 4| during intermittent halt cycles. The coil 42 is used only in order to provide additional ampere turns that may be needed in order to secure a safe picking-up operation. It should be understood, however, that the additional coil 43 can be eliminated if the coil 42 is rated for providing alone the necessary pick-up flux when energized by alternating current. It is likewise possible to use only part of coil 42 or 4| during the pick-up performance. It is presumed in the embodiment c! Fig. 2 that the start contact I! closes only temporarily so that the flow of alternatingcurrent through coils 42 and 42 ceases shortly after the holding contact i is closed. In order to secure such an interruption of the alternating pick-up current in cases where the start contact I! might be held closed longer than desirable, for instance if the starting contact is manually actuated, an interlock contact may be provided in an electromagnetic device for automatically opening the alternating-current circuit at the proper moment. Modifications of the justmentioned kind are incorporated in the embodiment illustrated in Fig. 3 and described presently.

According to Fig. 3, the leg I of the magnetic structure is provided with two series-connected coils 44 and 45, of which the latter has a tap at the point marked II. The common midpoint of the two coils is connected to the line terminal Ti 0! the device for attachment to the lead Ll oi. an alternating-current line. Two valve means i0 and II are connected across the coils 44 and 45, and a circuit point I! between the two valves is in connection with a resistor [2. The armature 2 of the device controls a holding contact I and also a normally closed interlock contact H. The start and stop contacts 01 the device are denoted by I5 and I4, respectively.

When the start contact [I is closed, an alternating-current circuit is completed from terminal Tl through the upper portion oi coil 45 to point I, thence through interlock contact ll, start The energizing circuit for coils 4| and contact ill and stop contact II to the other terminal T2 oi. the device, the latter being attached to the other lead L2 of the altemating-current line. The alternating-current magnetization produced by the coil portion between terminal TI and tap point It causes the armature 2 to be picked up. This, in turn, causes, first, the closing of the holding contact 6 and shortly thereafter the opening of the contact l'l. As soon as the holding contact 6 is closed, coils N and 45 become energized in a circuit that extends from terminal Ti in parallel through coil 44 and coil 45, rectifiers l and II, respectively, resistor l2, holding contact 8 and stop contact ll.

In the embodiment according to Fig. 3, the ampere turns of the upper portion of coil 45 during pick-up performance are larger than the ampere turn of coils 44 and 45 during the holding performance. This difference is due to the iact that the current limiting resistor 12 is eflective during the holding performance and also due to the fact that the current is then further reduced by the then increased impedance of the coils l4 and 45. By properly proportioning the components of the coil circuit, it is possible to eliminate the resistor i2 entirely, for instance by winding suiilcient turns and suflicient impedance into the coils 44 and 45 of the relay.

Other modifications than those specifically described can be applied by those skilled in the art without departing from the essential features of the invention as set forth in the claims annexed hereto.

I claim as my invention:

1. An electromagnetic device for alternatingcurrent operation, comprising a magnetic circuit having a substantially E-shaped and substantially non-remanent magnet structure with a center leg and having an armature biased away from said structure, a normally open holding contaot controlled by said armature, two series-connected coils disposed on said center leg for cumulative magnetization of said magnetic circuit, two rectifiers series-connected with each other across said two coils so as to form a closed circuit together with said coils, a normally closed stop contact, two alternating-current terminals connected to said closed circuit at midpoint between said rectifiers and a midpoint between said coils respectively, said holding contact and said stop contact being series-arranged relative to each other and interposed between said terminals and said closed circuit, said rectifiers having mutually opposing polarity relative to said terminals and said closed circuit being rated for providing unidirectional magnetization of said magnetic circuit in an amount less than required for picking up the relay but suflicient for holding it picked up, and a normally open start contact connected on the one hand to a circuit point between said stop contact and said holding contact and on the other hand to a point of one of said coils spaced from said coil midpoint so as to pass alternating current through the latter to provide pick-up magnetization for the relay.

2. An electromagnetic device for alternatingcurrent excitation, comprising a magnetic circuit having a substantially E-shaped and substantially non-remanent magnet'structure with a center leg and having an armature biased away from said structure, a normally open holding contact controlled by said armature, three seriesconnected coils disposed on said center leg, two rectifiers series-connected to each other across two adjacent ones of said coils, two alternatingcurrent supply leads, one oi said leads being connected to a point between said two coils, said other lead being connected to a point between said rectifiers, a normally closed stop contact, said holding contact and said stop contact being series arranged relative to each other and disposed in at least one of said leads, a normally open start contact connected on the one hand to a point between said stop contact and said holding contact and on the other hand to a point of said third coil spaced from said other coils so as to pass, when closed, an alternating current through said third coil and one of said other coils in order to cause picking-up of the device, said two rectifiers having mutually opposing polarities relative to current flowing between said leads, and said two adjacent coils and said rectifiers being rated for providing energization below the pick-up value but sufficient to hold the device after closing of said holding contact.

3. An electromagnetic device for alternatingcurrent excitation, comprising a magnetic circuit having a substantially E-shaped and substantially non-remanent magnet structure with a center leg and having an armature biased away from said structure, a normally open holding contact controlled by said armature, two series-connected coils disposed on said center leg, two rectifiers series-connected with each other across said two coils to form a closed circuit together with said coil, a normally closed stop contact, a currentlimiting impedance member, two alternating-current terminals connected in series with said stop contact and said holding contact and said impedance member to points of said closed circuit located respectively between said coils and between said rectifiers so as to provide unidirectional excitation for said coils limited to be insufficient for picking up the device but suiiicient for holding it picked up, said two rectifiers having mutually opposing polarities relative to current flowing between said terminals, and a normally open start'contact connected on the one hand to a circuit point between said stop contact and said holding contact and on the other hand to a point of one of said coils spaced from the other coil so to permit passing alternatingcurrent through said one coil to provide pick-up magnetization for the relay.

4. An electromagnetic device for alternatingcurrent excitation, comprising a magnetic circuit having a substantially E-shaped magnet structure with a center leg and having an armature biased away from said structure, a normally open holding contact controlled by said armature, three series-connected coils disposed on said center leg, two rectifiers series-connected with each other across two adjacent cores of said coils to form a closed circuit together therewith, a normally closed stop contact, a current-limiting impedance member, two alternating-current terminals connected in series with said stop contact and said holding contact and said impedance member to points of said closed circuit located respectively between said two coils and between said rectifiers so as to provide unidirectional excitation for said coils limited to be insufilcient for picking up the device but sumcient for holding it picked up, and a normally open start contact connected on the one hand to a point between said stop contact and said holding contact and on the other hand to a point of said third coil spaced from said other coils so as to pass, when closed, an alternating current through said third coil and 7 one of said other coils in order to cause pickingup of the device.

5. An electromagnetic device ior alternatingcurrent exic'tation, comprising a magnetic circuit having a substantially E-shaped magnet structure with a center leg and having an armature biased away from said structure, a normally open holding contact and a normally closed interlock contact both controlled by said armature, two series-connected coils disposed on said center leg, two rectifiers series-connected with each other across said two coils to form a closed circuit together with said coils, said rectiilers having the same polarity of connection relative to said closed circuit, a normally closed stop contact, a current-limiting impedance member, two alternating-current terminals connected in series with said stop contact and said holding contact and said impedance member to points of said closed circuit located respectively between said coil and between said rectifiers o as to provide unidirectional excitation for said coils limited to be insufficient for picking up the device but sufllcient for holding it picked up, a normally open start contact connected, on the one hand, to a circuit point between said stop contact and said holding contact and, on the other hand, to one of said coils in series with said interlock contact so that, when start contact is closed, a temporary alternating current is passed through said one coil for causing the device to pick up.

6. An electromagnetic device for alternatingcurrent excitation, comprising a magnet structure, an armature biased away from said structure, a normally open holding contact and a normally closed interlock contact both controlled by said armature, two series-connected coils disposed on said structure for cumulative magnetization of the latter, two rectiflers series-connected with each other acros said coils to form a closed cir- 8 cnit together therewith, said rectiiiers having the same polarity of connection relative to said closed circuit, a normally closed stop contact, a currentlimiting impedance member, two alternating current terminals connected in series with said stop contact and said holding contact and said impedance member to points of said closed circuit located respectively between said coils and between said rectiflers so as to provide unidirectional excitation for said coils limited to be insumcient for picking up the device but suiiicient for holding it picked up. and a normally open start contact connected, on the one hand, to a circuit point between said stop contact and said holding contact and, on the other hand, to an intermediate point of one oi said coils, said interlock contact being disposed between said start contact and said latter point, so that part of said one coil is temporarily energizedby alternating current to cause picking up of the device when said start contact is closed.

OWEN L. TAYLOR.

REFERENCES CITED The following references are of record in the flie of this patent:

UNITED STATES PATENTS 

